This invention relates to a flame retardant comprising phosphorus-containing condensation products.
Organophosphorus or organohalogen compounds have been used as a flame retardant for synthetic resins as disclosed in, for example, U.S. Pat. Nos. 3,247,134, 3,262,894, 3,278,464, 3,359,220, 3,368,916 and 3,372,141; British Pat. Nos. 1,015,212, 1,094,723, 1,108,064; and Belgian Pat. No. 709,417. However, when the conventional organophosphorus compounds are added to resins in an amount sufficient to impart flame retardancy, there are disadvantages that properties of the resin, such as heat resistance and impact strength are reduced.